Suspect J

[gencon]

18 yrs ago had a system put in by a highly respected contractor. Design is two story 2400 ft, very tight, good and properly placed windows/overhangs, etc. Came back with use either 3.0 or 3.5 ton AC, furnace is gas, 115000 BTU. I choose 3.5; never a substitue for cubic inches?

Problem: System has always short cycled. Changed thermostates, no vent nearby or directed at. Even in 25 deg winter, system will heat for 5-8 min, turn off and come back on in 10 mins.
On 95 deg summer, same pattern, AC runs for 5-10 min, turns off, cuts back on in 8 to 10 minutes.
System has always work well, no maintenace issues, etc.

My conclusion is it too BIG??
Should I replace wtih 3 ton and downsize the furnace to 80k btu's or so,.

HELP please, I have talked to 3 pros about the situation and got three answers; one was so far out to suggest that the wiring had reversed polarity??
help for the pro's please
thx
gn

[beenthere]

Have a load calc done again.

Sounds like some one just guessed, and told you they did a Manual J.

Your seeing the out come of that.

You can click on the bulls eye and do your own.

[obxtech]

Don't sound like you have talked to a pro yet, anyone that will tell you anything without performing a heat load calculation are just guessing, have a heat load done and then a pro can size it properly with out a bunch of guess work that probably wont work any ways.

[troyorr]

You have lived with this system for 18 years and it never worked right? Has the system maintained a comfortable temperature in the living spaces? Polarity probably isn't the issue with an 18 year old equipment.

[Twilly]

YES and No.

[gencon]

I was hoping to get some serious comments.
beenthere/obxtech: There was a load calcu done, it came in a little over 3.0T.

troyorr; I stated "the system has always worked well". Maybe thats not clear enough and I can expand on that; the temp control for heat and cold holds to less than 1 deg. The digital readout on the Honeywell thermo never varys and a cseperate temp readout confirms that the control is less the -/+ 1 deg.

twilli3967; yes and no?? To complicated for me; please expand.
thanks

[chillbilly]

You did get good advice from the previous posters.

Redo the load and be very methodical so as not to miss anything that could have been missed.
Check EVERYTHING including system configuration options, location,and orientation of returns, controls, duct sizing, etc.


Short cycling can be attributed to more than just improper load considerations but that would be the place to start if you are sure that the system operating specs are being satisfied.


Even "highly respected" contractors screw up.

[beenthere]

What did the heat load come out to.

Have you check your humidity level in the summer.

[gencon]

dont recall the heat load. Being in northern Fl and on the coast, AC was the main enphasis. Humidity control seems fine, the condensate pipe has a "steady" stream of water coming out of it. cooing/Heating cost have been better than expected.
gn

[beenthere]

If you've a;ways used digital stats with it, you may want to have the cph decreased.

[Hroper]

How many CFM's is the blower doing?